The present invention relates to a semiconductor device manufacturing apparatus and a semiconductor device manufacturing method and more particularly to a semiconductor device manufacturing apparatus and a semiconductor device manufacturing method suitable for monitoring the conditions of reaction products produced during a processing in the apparatus.
Conventional dry etching apparatus have a problem that, as the number of wafers processed increases, the amount of dust generated increases, thereby destabilizing the process, gradually deviating the process condition from the initial state resulting in unfavourable products, and reducing the yield. It is considered the reason for this is that reaction products are deposited on the inner walls of the processing chamber and on the surface of components, and dust particles are produced from the reaction products, destabilizing the process. The process destabilization may also result from other causes.
It has been found that cleaning the apparatus to remove the deposited reaction products (hereinafter referred to as "deposited materials") recovers the yield, but usually this requires exposure of the process chamber to the air. Once the apparatus is exposed to the air, however, it is necessary to perform evacuation again and to set the conditions for process stabilization before .the wafer processing is restarted. This results in a lowering of the working ratio (efficiency) of the apparatus.
Because lowering the frequency of the chamber cleaning lead to an improved working ratio of the apparatus, it is important to make a correct decision as to the time to perform the cleaning, and to perform the cleaning in such a way as to make it possible to increase the time before cleaning is needed again as along as possible. Determining the correct time for cleaning, however, is difficult under the present situation. Among the methods of determining the cleaning time are one in which a dummy wafer is processed and the amount of dust adhering to it is taken as a reference, and one in which the amount of dust generated in the apparatus is monitored. The difficulty with these methods lies in the fact that there are large variations in dust generation and the amount of dust adhering to the wafer is unstable.
Studies have been conducted to determine process requirements for suppressing the generation of deposited materials to a minimum level and to determine kinds of special gases suited for removing deposited materials. For this purpose, it is necessary to examine the state of deposited material adhering to the chamber, as well as the analysis of the deposited material itself.
Though the process chamber is exposed to the air to sample the deposited material for analysis, it is impossible to analyze the deposited material while the process is under way. The examination of the deposited material, therefore, is greatly restricted at present. It is also impossible to investigate how the deposited material is being produced with the lapse of time. It is therefore necessary to develop a method of determining the amount of deposited material and monitoring the state of deposition without exposing the apparatus to the air.
Among the methods of measuring the amount of deposits or reaction products, there is a method in which a reflector is installed inside the process chamber, light is projected through a window formed in the chamber, and the reflection factor is measured to estimate the amount of deposited material in the chamber, as described in Japanese Utility Model Publication No. 26737/1993.
Other related methods are disclosed in Japanese Patent Laid-Open No. 183919/1986, 276657/1991 and 12251/1992.
A conventional technique using a reflector needs an optical path from the window to the reflector, restricting the location of measurement inside the chamber. In apparatuses, such as a microwave plasma etching apparatus, which require that a window is provided and that the chamber is enclosed with an electromagnet, it is difficult to add a flange to the side of the chamber. It is also difficult to examine the composition of the deposited material and how it adheres to the chamber, as well as the amount of deposited material.